Wednesday, September 27, 2006

Finetuning the 303-boards

We tried out some alternative components on the Dada-JPE 303 boards.

- The trimmer-pots were replaced with Bourns 25 turn pots that will make a more precise calibration possible
- The resitors in the endstage were replaced with high-recision 0,3 Ohm 1% 5W resistances

Joost also made a board with reduced current-limiting (3 diodes for MR105/106).

The results are excellent!

Maximum power at full load (both channels with the Dada-JPE PSU board):

50W/8Ohm 28W/4Ohm (normal version)
52W/8Ohm 81W/4Ohm (high-current version)

The - 1dBV points are between 27Hz and 27KHz in both versions at full load.

Stefaan & Joost


Anonymous Anonymous said...


I'm wondering if it's possible to replace the light in the quad 33 and 303 with LED's, which are much quiet and easier to find.

Thanks a lot anyway for this blog, Hugues.

3:57 PM  
Anonymous Anonymous said...

Do not loose the screws of the 303. They are NOT metric!


10:30 AM  
Blogger Stefaan said...

It is very well possible to replace the lamps in a 33 or a 303 with leds.

For the 33: use a white led with a 1,2K resistor in series. Connect the LED to the DC-voltage (NOT the AC from the transformer like the lamp).

For the 303: use a red LED with a 4K7 resistor in series.

Kind regards, Stefaan

11:13 AM  
Blogger Stefaan said...

4BA x 1/4" screws for Quad 303/405 ao. are available in the Dada Webshop


11:15 AM  
Anonymous Anonymous said...


I'd like to know what is the purpose of the fifth output on the power board of the quad 33 ( see pics):

Should it be grounded? ( on my quad 303 the 2nd and 4th pin are connected )

Hugues ( thanks for the LED references... )

9:58 PM  
Anonymous Anonymous said...

Hello Hugues, the output was there for switching power amps by means of a relay. Quad removed this output on later (from serial 80.000)models of the 33. To lower the noise and the hum, this output and the components on the power supply Pcb should be removed. Do not connect this pin to ground, ther will be a short circuit.

Regards Joost Plugge

2:42 PM  
Anonymous Anonymous said...


It's interesting. and they never had mounted this relay in the quad 303 ?

I'll take out those parts next time I open my quad 33...

thanks, Hugues

3:33 PM  

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